I like to hike and I'm most interested in outdoor photography. Landscapes mostly and some wildlife/nature/flower type stuff. I've been reading up on polarizing, warming, ND, and UV filters. From what I gather, I buy a 52mm filter because my lens is 52mm (Nikon D5000 w/ 18-55m kit lens). The filters are supposed to be screw on. However, when I look at the end of my lens, I don't see any type of thread or anything for the filter to screw onto. Can someone explain how this works? I don't want to order the wrong filters. Any other filter advice is welcome as well.

also, if you plan on upgrading lenses in the future dont get a real expensive filter in 52mm, i believe a cheaper filter will work just fine with the cheaper lens. or get a 62-72mm decent filter and get a stepdown ring, so when you upgrade you can still use the filter